Elucidating acetogenic H₂ consumption in dark fermentation using flux balance analysis

In this study, a flux balance analysis (FBA) was adopted to estimate the activity of acetogenic H₂-consuming reaction. Experimental data at different substrate concentrations of 10, 20, and 30g COD/L showing the lowest, medium, and highest H₂ yields, respectively, were used in the FBA to calculate the fluxes. It was interesting to note that the hydrogenase activity based on R12 (2Fd⁺+2H⁺→2Fd²⁺+H₂, ferredoxin (Fd)) flux was most active at 10g COD/L. The flux of R17 (4H₂+2CO₂→CH₃COOH), a mechanism for reutilizing produced H₂, increased in steps of 0.030, 0.119, and 0.467 as the substrate concentration decreased. Contradictory to our general understanding, acetate production found to have a negligible or even negative effect on the final H₂ yield in dark fermentation.